5,854 research outputs found
Fractional Brownian motion with a reflecting wall
Fractional Brownian motion, a stochastic process with long-time correlations
between its increments, is a prototypical model for anomalous diffusion. We
analyze fractional Brownian motion in the presence of a reflecting wall by
means of Monte Carlo simulations. While the mean-square displacement of the
particle shows the expected anomalous diffusion behavior , the interplay between the geometric confinement and the
long-time memory leads to a highly non-Gaussian probability density function
with a power-law singularity at the barrier. In the superdiffusive case,
, the particles accumulate at the barrier leading to a divergence of
the probability density. For subdiffusion, , in contrast, the
probability density is depleted close to the barrier. We discuss implications
of these findings, in particular for applications that are dominated by rare
events.Comment: 6 pages, 6 figures. Final version as publishe
Extinction transitions in correlated external noise
We analyze the influence of long-range correlated (colored) external noise on
extinction phase transitions in growth and spreading processes. Uncorrelated
environmental noise (i.e., temporal disorder) was recently shown to give rise
to an unusual infinite-noise critical point [Europhys. Lett. 112, 30002
(2015)]. It is characterized by enormous density fluctuations that increase
without limit at criticality. As a result, a typical population decays much
faster than the ensemble average which is dominated by rare events. Using the
logistic evolution equation as an example, we show here that positively
correlated (red) environmental noise further enhances these effects. This
means, the correlations accelerate the decay of a typical population but slow
down the decay of the ensemble average. Moreover, the mean time to extinction
of a population in the active, surviving phase grows slower than a power law
with population size. To determine the complete critical behavior of the
extinction transition, we establish a relation to fractional random walks, and
we perform extensive Monte-Carlo simulations.Comment: 11 pages, 12 figures, Final versio
Investigation of the dc-excited xenon laser final report, 24 mar. 1964 - 24 mar. 1965
Electron energy spectra in gas laser discharges and investigation of new discharge configuration
Valley current characterization of high current density resonant tunnelling diodes for terahertz-wave applications
We report valley current characterisation of high current density InGaAs/AlAs/InP resonant tunnelling diodes (RTDs) grown by metal-organic vapour phase epitaxy (MOVPE) for THz emission, with a view to investigate the origin of the valley current and optimize device performance. By applying a dual-pass fabrication technique, we are able to measure the RTD I-V characteristic for different perimeter/area ratios, which uniquely allows us to investigate the contribution of leakage current to the valley current and its effect on the PVCR from a single device. Temperature dependent (20 – 300 K) characteristics for a device are critically analysed and the effect of temperature on the maximum extractable power (PMAX) and the negative differential conductance (NDC) of the device is investigated. By performing theoretical modelling, we are able to explore the effect of typical variations in structural composition during the growth process on the tunnelling properties of the device, and hence the device performance
Intrinsic localized modes in the charge-transfer solid PtCl
We report a theoretical analysis of intrinsic localized modes in a
quasi-one-dimensional charge-transfer-solid (PtCl). We discuss strongly nonlinear features of resonant Raman
overtone scattering measurements on PtCl, arising from quantum intrinsic
localized (multiphonon) modes (ILMs) and ILM-plus-phonon states. We show, that
Raman scattering data displays clear signs of a non-thermalization of lattice
degrees-of-freedom, manifested in a nonequilibrium density of intrinsic
localized modes.Comment: 4 pages, 4 figures, REVTE
International Stock Market Efficiency: A Non-Bayesian Time-Varying Model Approach
This paper develops a non-Bayesian methodology to analyze the time-varying
structure of international linkages and market efficiency in G7 countries. We
consider a non-Bayesian time-varying vector autoregressive (TV-VAR) model, and
apply it to estimate the joint degree of market efficiency in the sense of Fama
(1970, 1991). Our empirical results provide a new perspective that the
international linkages and market efficiency change over time and that their
behaviors correspond well to historical events of the international financial
system.Comment: 21 pages, 2 tables, 6 figure
Nanoparticles for microbial control in water: mechanisms, applications, and ecological implications
Waterborne microbial contamination poses significant threats to public health and environmental sustainability. Traditional water treatment methods, while effective to a certain extent, are often limited in their ability to completely eradicate microbial pathogens and mitigate emerging challenges such as disinfection by-products and microbial resistance. In recent years, nanoparticles have emerged as promising candidates for microbial control in water treatment due to their unique physicochemical properties and antimicrobial efficacy. This review provides a comprehensive examination of the use of nanoparticles for microbial control in water treatment, focusing on their antimicrobial mechanisms, applications, and ecological implications. The review discusses the types of nanoparticles commonly used in water treatment, including silver nanoparticles, copper nanoparticles, titanium dioxide nanoparticles, and carbon-based nanoparticles, and examines their antimicrobial mechanisms, such as cell membrane damage, reactive oxygen species generation, and interference with microbial metabolic processes. Furthermore, the review explores the applications of nanoparticles in the disinfection of drinking water, wastewater treatment, water purification in remote areas, and biofilm control. Additionally, the ecological implications of nanoparticle-based water treatment, including nanoparticle release into the environment, environmental persistence, toxicity to non-target organisms, and regulatory challenges, are critically evaluated. Finally, future perspectives and challenges in nanoparticle-based water treatment, such as enhanced nanoparticle synthesis and stability, development of sustainable treatment technologies, integration with conventional methods, and addressing knowledge gaps, are discussed. Overall, this review provides valuable insights into the potential of nanoparticles as innovative tools for addressing microbial contamination in water treatment while highlighting the need for further research and sustainable practices to ensure their safe and effective implementation
- …